Flow measuring device



Aug. 9, 1966 1.. J. BERGER, JR

FLOW MEASURING DEVICE 2 Sheets-Sheet 1 Original Filed Jan. 31, 1962INVENTOR. LEO J. BER6ER,JR.

ATTOQNEY 2 Sheets-Sheet 2 Original Filed Jan. 31, 1962 AND VALVINGDEVICE S u 5 P 6 5 a. U. R 6 6T NC m "1 c 2 L A N m S ATMOSPHERIC 0RREFERENCE PRESSURE Fig. 4

mvsmoa LEO J. BERGER,JR.

BY Qzama Q.

ATTORNEY United States Patent 3,264,870 FLOW MEASURING DEVJICE Leo J.Berger, In, Madison Heights, Mich, assignor to Scans Associates, Inc.,Livonia, Mich, a corporation of Michigan Griginal application Jan. 31,1962, Ser. No. 170,109, now Patent No. 3,150,525, dated Sept. 29, 1964.Divided and this application July 31, 1964, Ser. No. 386,637 2 Saints.(Ql. 73205) The present application is division of my co-pendingapplication, Serial No. 170,109, filed on January 31, 1962, for PressureIndicating Device, now US. Patent No. 3,150,525.

This invention relates to pressure indicating devices used incombination with pressure amplifying devices such, for instance, asdevices known in the trade as differential pressure cells for thepurpose of measuring flow of fluids.

Pressure indicating devices or pressure gauges usually include a handactuated by a pressure sensitive element, such as a diaphragm respondingto the difference of pressure on its respective sides, or a curvedhollow member tending to straighten out with the increase of pressure,with such pressure-responsive element being drivingly connected withsaid hand. The extent or distance through which the hand moves ismeasured on a graduated scale fixed within the device in such a mannerthat at atmospheric pressure, or other pressure set to be a startingpoint, the hand is at zero point, and its travel away from said pointindicates the pressure to be read in desired units in which the scale isgraduated.

I have found, however, that measurements made from such arbitrarily andrigidly set zero point are very misleading and in many cases result notonly in errors in read ings but also in improper functioning of thedevices operating in response to predetermined pressures. This isparticularly true when such pressure indicating devices operate incombination with pressure amplifiers intended to increase the precisionof pressure measurements. It should be understood that where suchpressure amplifying devices or pressure differential cells amplify acertain pressure and changes therein, they may also correspondinglymultiply the changes in the starting or zero pressure.

Changes in a starting or zero pressure may result from changes intemperature within the pressure test chamber, changes in barometricpressure, turbulences within the test pressure chamber and other causes.In cases when the actual or true pressure to be measured comes close tothe predetermined pressure limit at which certain functioning ofactuated devices occurs, the effect of the change in the startingpressure may cause operation of the pressureresponsive devices uncalledfor by the actual pressure, or may cause incorrect reading and anerroneous evaluation. Such results are particularly likely to occur whenpressure measurements are repeating, i.e. following one another, as inproduction testing, and the cycle of measuring and connected operationsis very short, such as being measured in seconds.

One such application, in which conventional pressure indicating devicescreate a number of very serious problems, is in systems for measuringpressure drop or the rate of pressure drop in test chambers or hollowparts for determining the amount or rate of leakage therefrom. Suchmeasurements are made in the use of systems well known in the art fortesting various hollow parts for leakage, such as may be caused byporosity of the material, casting flaws, improper welding, insufficientsealing of joints, or faulty workmanship. Such pressure measurements aremade at a relatively high rate for the purposes of eifi ciency ofproduction, with the entire measuring cycle being only a few seconds induration. Therefore, the

pressure within the hollow or cavity of the tested part, at which themeasuring cycle begins may not be sufficiently stable, being affected byturbulences, change of temperature of air due to the difference oftemperature between the air and the walls of the chamber, changes inatmospheric pressure, changes in altitude, ambient temperature, andsimilar causes.

One of the objects of the present invention is to provide an improvedpressure indicating device which gives pressure readings not from somerigid or unchangeable pressure level but from a starting point whichautomatically adjusts itself to the point with compensation for mistakesor parasitic influences caused by some of the conditions explainedabove.

Another object of the invention is to provide an improved pressureindicating device of the foregoing character without introducing otherproblems or increasing appreciably the costs involved.

A further object of the present invention is to provide an improvedpressure indicating device in which measurements are taken by reading onthe scale the distance of travel of a hand from another hand, with bothof said hands setting themselves at the same point at the beginning ofthe test or measuring cycle, and withone hand becoming, in effect,locked at the starting point.

A still further object of the present invention is to provide, in amanner of a modification, a pressure indicating system having a floatingscale adapted to adjust itself to have its zero mark come to theposition corresponding to the actual starting pressure rather than acertain rigidly predetermined zero point.

A still further object of the invention is to provide an improvedpressure indicating device used in combination with pressure amplifiersor differential pressure cells, particularly but not exclusively for thepurpose of leakage testing systems, and thereby making it possible toutilize more fully the ability of such amplifiers to permit evaluationof test results to the accuracy of plus-minus .02" of water.

FIG. 1 is a front view of the improved pressure indicating deviceembodying the present invention, with both the reference pressureindicating hand and the measured pressure indicating hand of the devicebeing set in registry on the mark corresponding to the referencepressure.

FIG. 2 is a view similar in part to FIG. 1 but showing the referencepressure indicating hand remaining at the mark indicating the referencepressure and with the measured pressure indicating hand in a position atthe point indicating the magnitude of the measured pressure.

FIG. 3 is a view of a pressure indicating device embodying the presentinvention in a modified construction and shown in combinat on with adifferential pressure cell and with a timer device for the purpose ofmeasuring the rate of pressure change.

FIG. 4 shows a pressure indicating device embodying the presentinvention in a still further modified construction.

Referring to the drawings, there are shown therein, by way of example,three embodiments of the present invention. FIGS. 1 and 2 illustrate apressure indicating device particularly advantageous for use inmeasuring rates of pressure changes in leakage testing systems. It willbe understood, however, that pressure indicating devices shown in saidfigures, as well as devices of modified constructions embodying thepresent invention are not limited to such application and may be usedfor pressure measurements in numerous other applications and under manyconditions. Pressure indicating devices embodying the present inventionmay be used singly or in combination 'with pressure differential cellsor devices amplifying pressure variations for more convenientmeasurements. Such measurement may be made to determine momentarypressures, i.e. to indicate pressure existing at a certain moment, aswell as to determine the rate of pressure changes, such, for instance,as is usually done in leakage testing systems.

In leakage testing systems my improved pressure indicating devices areused in connection with differential pressure cells for the purposes ofindicating the rate of leakage in a tested part, such as in anautomobile engine cylinder block, or other hollow casting, riveted orwelded tanks, and the like. The degree or rate of leakage is usuallyused as an indication of the quality of castings or of the welded seams,tightness of riveted joints, and even porosity of the metal itself. Itshould be appreciated that in many instances the leakage is so small andthe measuring period is so short (for the purpose of speed of testing inquantity production) that the existing instruments would be unable togive any appreciable indication of change in pressure. Accordingly, thedifferential pressure cells used in leakage testing systems operate tomagnify the pressure drop within the tested part and change the pressuredrop to pressure rise for more convenient measuring. In testing, airunder pressure is pumped into a test part to a certain predeterminedpressure, such as 100 pounds per square inch, whereupon the part isisolated from the source of such pressure and the rate of pressure dropwithin such part is measured through a predetermined time interval suchas seconds. Suppose, for the purpose of example, that it is determinedthat a pressure drop of one pound per square inch in 10 seconds is themaximum permissible drop, and that should a greater drop be indicated,the part is to be rejected. In conventonal instruments used in suchleakage testing systems, the pressure indicating devices are soconstructed that pressures are measured or read from a starting pointwhich corresponds to the predetermined test pressures intended to bepumped into the tested part, 100 pounds per square inch in the examplegiven.

I have found that such measurements, although commonly used, contain aserious source of error, causing, in many situations, such measurementsto be wholly unreliable and a cause of passing defective parts as wellas rejecting completely sound parts. I found that the source of sucherror lies in the fact that under the above described conditionsmeasurements are taken and readings are made not from a starting pointwhich represents a definite and stable pressure, as it is mistakenlypresumed to be, but from a point and pressure which may be higher orlower than the presumed pressure. Obviously, a measurement taken from anuncertain or varying starting point is similarly uncertain and,therefore, unreliable.

In the example given, since measurements are taken from the startingpoint of a presumed 100 pounds per square inch pressure, this pressuremay be termed for the purposes of the present invention as the referencepressure. erence pressure may be due to a number of causes, bothpeculiar to a particular application, as well as independent thereof.For instance, it has been found that in leakage testing systems inpumping the air into the test part to the predetermined pressure such as100 pounds per square inch, the time required to raise the pressure from99 lbs. to 100 lbs. may be many times as long as the time require toraise the pressure in such part from 9 lbs. to 10 lbs. Accordingly, inorder to save time, the pumping system is set to pump the air not to 100pounds per square inch pressure but to 102 pounds or an even higherfinal pressure, cutting off the period of filling toward its end atapproximately the moment when the pressure in the tested part is aboutto reach but has not yet reached the predetermined pressure of 102pounds, in the expectation that the pressure at the moment of cuttingoff the pumping means would be approximately 100 pounds. Therefore, theactual pressure at which the part is tested is somewhat uncertain andvarying. The condition of turbulence due to the flow of air into thepart I found that changes or uncertainties in such refstill continues atthe instance of starting the test and, therefore, it adds to the aboveuncertainty. Furthermore, the tested parts may be at a temperaturedifferent than the temperature of the air as it reaches the tested part.Usually the temperature of the tested part is considerably lower thanthat of the air. Consequently, when the part is filled with air which isstill moving within the part, the air cools rapidly and its temperaturedrops, causing a corresponding drop in pressure. Changes in barometricpressure may also effect the pressure indicating instruments and theirreading of the presumed pounds reference pressure.

Under the conditions described above, the drop in the reference pressureduring the filling and pressure-stabilizing time may be considarable andin some instances may approach one pound per square inch, i.e. thepermitted maximum drop due to leakage. In such a situation a perfecttest part would be rejected by the system for showing what is presumedto be but actually is not leakage. In order to give a correct result,the reference pressure from which the pressure drop is to be measuredshould be not 100 pounds per square inch but the actual pressureexisting within the test part at the start of the test period. However,since such actual or true reference pressure is varying, itsdetermination in advance is exexceedingly difiicult, if not actuallyimpossible.

In accordance with the invention, the pressure measurements are takennot from a certain predetermined point related to atmospheric pressure,but from a starting point which corresponds to the actual pressure,whatever it may be at the moment of starting the test, with suchstarting point being automatically and correctly set by the pressureindicating device at the beginning of each test cycle, i.e. for eachtested part.

In accordance with the invention, I make such pressure measurementsfirst by measuring the true pressure existing within the tested parts atthe instant of starting the test, retaining such measurement reading onthe device, and thereupon making measurements from such starting pointor reference pressure. Thus, in my improved method of pressuremeasurements, I measure or set the reference pressure, in effect, foreach test period.

Referring specifically to the drawings, the pressure indicating devicewith which the above method is practiced in leakage testing systemscomprises a suitable casing generally designated by the numeral 10, inwhich there are hingedly mounted at a hinge point 11 a referencepressure indicating hand 12 and a measured pressure indicating hand 13.Pressure-responsive means, in the present embodiment expansible bellows14, are drivingly connected with the aid of links 15 and 16 with thehand 12, while second pressure-responsive means, in the present instancealso expansible bellows 17, are drivingly connected with the aid oflinks 18 and 19 with the hand 13. The links 15 and 18 are hingedlymounted at their ends at pivot points 20 and 21, respectively. Therespective linkage driving connections of the hands 12 and 13 are soconstructed and adjusted that when the bellows 14 and 17 are subjectedto the same pressure, the hands 12 and 13 come in a position ofregistry, such as shown in FIG. 1. The exact point at which the hands 12and 13 come to registry depends on the pressure to which the bellows 14and 17 are subjected.

A conduit 25 is connected to the tested part and to the bellows 14 and17 with the aid of branch conduits 26 and 27, respectively. Within thebranch conduit 26 there is operatively interposed a valve 28 adapted tointerrupt the communication of the bellows 14 with the conduit 25 and,therefore, with the tested part and the pressure existing therein.

In operation, with the valve 28 being open, the bellows 14 and 17 becomesubjected to the same pressure, and the hands 12 and 13 come into aposition of registry at a point corresponding to such pressure, as shownin FIG. 1. Thus, both the hand 12 and the hand 13 indicate the startingpoint or the reference or starting pressure. Thereupon, as the valve 28closes, the reference pressure is retained in the bellows 14, retainingthe reference pressure indicating hand 12 in its set position. With thebranch conduit 26 and the bellows 14 being air tight, the hand 12remains in such position for a sufficiently long period of time tocomplete the test. On the other hand, the bellows 17, being incommunication with the tested part through the conduit 25, is subjectedto the changes in pressure in said tested part. With such pressuredropping and the bellows 17 contracting, the hand 13 begins to move tothe right, usually continuing such movement during the entire testperiod. The position of the hand 13 at the end of such period indicatesthe pressure existing at the end of the test period.

Now, the pressure drop within the tested part would be measured by thedistance between the hands 12 and 13 rather than by the distance betweenany arbitrarily set zero or other point and the hand 13. A scale such asthe one indicated by the numeral may be provided in the device. It willnow be clear, however, that the position of such scale in my improvedpressure indicating device is only of relative importance, and its valueis primarily in giving a reading in the number of graduations betweenthe hands. Therefore, placing any numerals on the scale beginning with azero point is undesirable as providing possibilities of confusion.Furthermore, it is desirable to fix the scale in the casing 10 in such amanner that the hands 12 and 13 always operate intermediately of theends of such scale and do not actually reach the stems 31 and 32. Thelatter may be provided, in addition to suitable stops on the linkages,merely to prevent the hands 12 and 13 hitting the wall of the casing orother parts of the device and damaging their delicate points.

A switch device generally designated by the numeral is provided and isoperatively mounted on the casing 10 with the aid of a suitable bracket,such as 41. A terminal 42 is provided on the disc 43, while a secondterminal 44 is carried by a bracket 45 connected through a link 46 tothe hand 13. The disc 43 is connected through a link 47 and anadjustment crank 48 with the hand 12. A gear section 49 provided on thedisc 43 is engaged by a worm screw 50 carried by the crank 48 and usedfor the purposes of adjustment.

In FIG. 1 the terminals 42 and 44 are shown open, and the distancebetween them determines the amount of permissible maximum leakage. Thevalve 28 is also in the open position for the purposes explained above.

After closing the valve 28, which may be done through operation of atimer device such as that shown in FIG. 3, movement of the hand 13operates to carry the contact 44 toward the contact 42. If the distanceI is traveled and the limit position is reached by the hand 13 within ashorter period of time than the set time period controlled by a timerdevice (which may be operated by a separate electric circuit), thecontact 44 will reach the contact 42, this would indicate presence ofleakage in excess of said maximum, whereupon a visible or audible signalis made to operate, thus indicating that the tested part is defectiveand should be rejected. On the other hand, if the hand 13 does not reachthe limit position within the set time period, which would be the casewhen the test part is sound and has only permissible leakage, thecontacts 42 and 44 do not close, no reject signal is energized, and thepart will be accepted. FIG. 2 shows such a condition, it being presumedthat said figure illustrates positions of the parts of the device at themoment of expiration of the set test period. As indicated in FIG. 1, tocall for rejection of the test part the total travel of the hand 13within the test period should be 9 or more graduations. In FIG. 2 thehand 13 traveled with such period only 5 /2 graduations, indicating onlypermissible leakage and an acceptable part. This concludes one testcycle. To start a test on another part,

the same is connected to the system and filled with air under pressureas explained above. Thereupon, the valve 28 is open, with hands 12 and13 brought to registry, and the timer device again actuated to beinganother test cycle. For the purposes of operating the valve 28automatically, i.e. for opening it prior to the start of the testperiod, in order to bring the hands 12 and 13 in registery, as well asfor closing said valve in order to start the test period, automaticmeans may be provided in the system and controlled electrically. Thedetails of such a leakage testing system are to be disclosed in aseparate application.

FIG. 3 illustrates my improved pressure indicating device of a modifiedconstruction used to measure the rate of liquid flow through a conduit,as well as changes in such rate as may result from a variety of causessuch, for instance, as changes in the pressure head or in the size ofrestriction in the conduit, and the like. In FIG. 3 the conduit isdesignated by the numeral and is provided with a restriction or orifice56. Operation of said orifice 56 causes pressure drop from a pressure onits upstream side indicated by the character P to a pressure on itsdownstream side indicated by the character P For the purpose ofmeasuring the difference between such pressures, the actual valuesthereof may be immaterial, while the precise difference between thesetwo values is of importance. Accordingly, the amplifying and valvingdevice 60, being connected to the pressure zones on the opposite sidesof the orifice 56 as shown in FIG. 3, operates to give the differencebetween the pressures existing therein, rather than the value of each ofsuch pressures separately. Devices of this general type are well knownin the art and are usually referred to as differential pressure cells.Such devices usually amplify the difference between the two pressures towhich they are exposed. In the device of FIG. 3 the hands 12 and 13 aredrivingly connected to two separate pressure-responsive means, in thisembodiment diaphragms 57 and 58, through linkages similar to those ofthe construction of FIGS. 1 and 2. In accordance with the invention thediaphragms 5'7 and 58 are first subjected to initial difference betweenthe pressures on the opposite sides of the restriction or orifice 56, byopening the valve 28 and thus subjecting said diaphragms 57 and 58 tothe same pressure conveyed thereto from the amplifying and valvingdevice 60, and thus setting the hands 12 and 13 in registry at areference point or mark. Thereupon, the valve 28 is closed for retainingsaid initial or reference pressure acting on the diaphragm 57, butleaving diaphragm 58 subjected to the pressure conveyed thereto from theamplifying and valving device 60. As the difference between thepressures on the opposite sides of the restriction 56 changes due to acause such as mentioned above, the pressure conveyed to the diaphragm 58from the device 61 varies correspondingly, causing the hand 13 to moveon the scale 62 to a position indicating at any particular moment thechanged value of the difference between the pressures on the upstreamand downstream sides of the restriction 56. In measuring rapidly andrepeatedly a pressure differential drop or rise occurring within apredetermined time period, it is desirable to have the duration of suchperiod controlled automatically. Accordingly, a timer mechanismoperatively connected with the valve 28 for closing the sameautomatically after expiration of a predetermined period of time, may beprovided.

An important modification in the construction of the pressure indicatingdevice itself is found in eliminating the feature of the device of FIGS.1 and 2 wherein the graduated scale 30 is fixed to the casing 10 of thedevice and is graduated preferably without placing numerals thereon, asmentioned. With such a rigidly fixed scale, should the hands 12 and 13come in registry intermediately of two graduations, and the hand 13 atthe end of the test also come to a position between the graduations,

precise reading of the distance travelled by the hand 13 may bedifficult. In the construction of FIG. 3 such difficulty is eliminatedby providing a floating scale 62 carried by the hand 12, with its zeropoint being at the center line of the hand 12. With such a construction,when the hands 12 and 13 are in registry, the hand 13 will be always atzero on the scale, and, therefore, measurements can be read correctly onthe scale 62. It should be noted, however, that the zero position of thescale with respect to the casing may vary within the limits determinedby suitable stop means, such as stop stems 63 and 64.

FIG. 4 illustrates a pressure indicating device in which a hand forindicating the reference pressure is eliminated as such and issubstituted by a scale sector 70 hinged at 71 together with butindependently of the measured pressure indicating hand 13. The scalesector 70 is actuated by the diaphragm 57 through suitable linkage,while the measured pressure indicating hand 13 is actuated by thediaphragm 58. A conduit 72 having branch conduits 73 and 74 provides aconnection between the diaphragms 57 and 58 as well as with the conduit72. A valve 28 is interposed in the branch conduit 73 to disconnect itfrom the source of reference pressure. The closed vessel 75 containingpressure to be measured is connected to the conduit 72, with a valve 76provided at the vessel 75 to disconnect the same from said conduit 72. Abranch conduit 77 provided with a valve 78 is connected to the conduit72. The conduit 77 may be open to the atmosphere or to a source of anydesired reference pressure. In the use of the device, the valve 76 isclosed and the valves 28 and 78 are open, thus subjecting the diaphragms57 and 58 to the same pressure and, therefore, bringing the hand 13 to azero point on the sector scale 70. Thereupon, the valves 78 and 28 areclosed, and the valve 76 is open, subjecting the diaphragm 58 to theaction of measured pressure within the closed vessel 75 and thusbringing the hand 13 to a position on the scale indicating the intensityof the measured pressure.

In pressure indicating devices having its hand such as 13 hinged at thecenter of the casing, instead of a scale sector a disc scale may beused.

It will now be seen that in this device the measurements will be read onthe scale from the zero point, but with such zero point being, ineffect, floating and adjusting itself to the point from whichmeasurements are being taken. Such zero point may approximatelycorrespond to standard atmospheric conditions to which pressuremeasurements are usually related, or it may be any point above or belowatmospheric pressure. But in all cases it will be the actual existingatmospheric or other reference pressure from which measurements aremade. By virtue of such expedient the pressure indicating deviceembodying the present invention provides within itself means whichcompensate for and eliminate errors in pressure indications and readingscaused by various conditions affecting atmospheric or other referencepressures from which measurements are taken as from starting points.

There is thus provided an improved pressure indicating device wherebythe objects of the invention listed above and numerous additionaladvantages are attained.

I claim:

1. An apparatus for measuring the rate of flow through a conduit havinga restriction therein, and changes in said rate, said apparatuscomprising an amplifying and valving device having one of its sidesoperatively connected to said conduit at the upstream side of saidrestriction and the other side connected to said conduit at thedownstream side of said restriction and adapted to produce pressuresrelated to the difference between the pressures existing on saiddownstream and said upstream sides, a pressure-indicating deviceconnected to said amplifying and valving device to receive therefrom thepressure related to said difference; said pressure-indicating devicecomprising an indicating member, a reference member, firstpressureresponsive means drivingly connected to said indicating member,second pressure-responsive means drivingly connected to said referencemember, the respective driving connections of said respectivepressure-responsive means adapted to set said indicating member on saidreference mark when both of said pressure-responsive means are subjectedto equal pressures, conduit means adapted to subject both of saidpressure-responsive means simultaneously to the action of pressureconveyed from said amplifying and valve device to set the indicatinghand on said reference mark, and valve means interposed in said conduitmeans and adapted to isolate the pressure-responsive means of thereference member from said amplifying and valving device and to retainthe pressure originally conveyed thereto for acting thereon and thus toretain said reference member in the position so reached but to maintainconnection of the pressure-responsive means of the indicating memberwith said amplifying and valving device for subjecting said means to thevarying pressure conveyed thereto from said amplifying and valvingdevice.

2. The apparatus defined in claim 1 and including an electric circuithaving a source of electric current, electrically operated meansconnected to said valve for closing and opening the same, and a timerdevice controlling said circuit and said valve actuating means tocontrol the test duration.

References Cited by the Examiner FOREIGN PATENTS 632,074 2/1935 Germany.

RICHARD C. QUEISSER, Primary Examiner.

1. AN APPARATUS FOR MEASURING THE RATE OF FLOW THROUGH A CONDUIT HAVING A RESTRICTION THEREIN, AND CHANGES IN SAID RATE, SAID APPARATUS COMPRISING AN AMPLIFYING AND VALVING DEVICE HAVING ONE OF ITS SIDES OPERATIVELY CONNECTED TO SAID CONDUIT AT THE UPSTREAM SIDE OF SAID RESTRICTION AND THE OTHER SIDE CONNECTED TO SAID CONDUIT AT THE DOWNSTREAM SIDE OF SAID RESTRICTION AND ADAPTED TO PRODUCE PRESSURES RELATED TO THE DIFFERENCE BETWEEN THE PRESSURES EXISTING ON SAID DOWNSTREAM AND SAID UPSTREAM SIDES, A PRESSURE-INDICATING DEVICE CONNECTGED TO SAID AMPLIFYING AND VALVING DEVICE TO RECEIVE THEREFOM THE PRESSURE RELATED TO SAID DIFFERENCE; SAID PRESURE-INDICATING DEVICE COMPRISING AN INDICATING MEMBER, A REFERENCE MEMBER, FIRST PRESSURE RESPONSIVE MEANS DRIVINGLY CONNECTED TO SAID INDICATING MEMBER, SECOND PRESSURE-RESPONSIVE MEANS DRIVINGLY CONNECTED TO SAID REFERENCE MEMBER, THE RESPECTIVE DRIVING CONNECTIONS OF SAID RESPECTIVE PRESSURE-RESPONSIVE MEANS ADAPTED TO SET SAID INDICATING MEMBER ON SAID REFERENCE MARK WHEN BOTH OF SAID PRESSURE-RESPONSIVE MEANS ARE SUBJECTED TO EQUAL PRESSURE, CONDUIT MEANS ADAPTED TO 